Studies are designed to improve our understanding of normal and abnormal visual function, with special emphasis on color vision. Basic response characteristics of human cones are undertaken using psychophysical and electrophysiological methods. The latter work is undertaken on a consortium arrangement with SRI International, Menlo Park, CA; it utilizes microelectrode recording methods, directly from monkey retina. They psychophysical work utilizes human subjects. Of special interest are (a) thresholds of chromatic discrimination as mediated by specific sensory channels; (b) principles of dichoptic chromatic interaction; (c) sources of residual red-green discrimination in human dichromats; and (d) the characteristics of the human blue-cone mechanism.